| In the third generation (3G) mobile telecommunication system, the input signal to the radio frequency power amplifier (RFPA) characterizes of non-constant envelope with high bandwidth. Under this condition, constant amplitude power supply to the RFPA will lead to significant power loss. To improve the system efficiency, one of the most promising methods is the envelope tracking (ET) technique, which can efficiently provide a varying supply voltage according to the envelope of the transmitted signal, such that the RFPA can nearly operate in its theoretical maximum efficiency region. Considering the high bandwidth and high efficiency requirement in ET power supply, there are many design challenges to be faced with. This thesis is dedicated to the system configuration, topologies and control strategies for the ET power supply.In this thesis, a linear amplifier and a switched-mode converter are connected in parallel at the output side to construct the ET power supply. The linear amplifier with high bandwidth operates as a voltage source, making the output voltage of the ET power supply follow the envelope of the transmitted signal. It is constructed by three-stage amplifier architecture. The switched-mode converter with high efficiency operates as a current source, providing most of the load current. It adopts a synchronous-rectification buck converter. A double-voltage-closed-loop voltage control strategy is proposed to regulate the output voltage of the linear amplifier, in which, the AC component of the output voltage is regulated by both the inner and outer voltage closed-loops, and the DC component of the output voltage is regulated by the outer voltage closed-loop. A pulse-width modulation (PWM) current control strategy is proposed for the switched-mode converter, aiming at making the switched-mode converter provide nearly all the output current, so that the linear amplifier only provides the switching frequency ripple current resulted by the switched-mode converter, thus the overall efficiency of the ET power supply can be improved. The PWM current control strategy has the advantage of constant switching frequency, providing the possibility of future paralleling of interleaved multiple switched-mode converter. The current control strategy is improved to further reduce the output current of the linear amplifier. The design of the key components in the ET power supply is discussed in this thesis as well as the design of the voltage regulators and current regulator. Meanwhile, the factors of affecting the output voltage ripple are pointed out.Finally, a prototype with average power of 37.5W and peak power of 75W is fabricated and tested in the lab. The simulation and experimental results are given to verify the effectiveness of the proposed topologies and control strategies for ET power supply. |
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